The present invention relates to a method of punching a flat cable.
In general, flat cables comprise at least one conductor zone defining the side of an empty intermediate zone whose midplane is designed to contain the punch axis; the diameter of the punch being as a general rule smaller than the width of said empty zone.
Such punching is intended to provide orifices for use as positioning references for subsequent operations of automatically soldering the cable to auxiliary electrical or electronic members such as connectors, circuits, . . .
Traditionally, a flat cable is punched by placing it so that one of its lateral edges presses against a flank that is secured to a fixed reference guide.
Where appropriate, a second flank placed facing the first provides resilient thrust against the other lateral edge of the cable so as to compensate for possible variations in width.
Nevertheless, the position of the midplane of the empty zone depends closely on the lateral positioning of the conductor zone and that is not completely unvarying along the length of the cable because of the manufacturing tolerances accepted for its margin, whereas the position of the punch axis is always unchanging since it is associated with the position of the tool.
Lateral offsets in the midplane of the intermediate empty zone can therefore give rise to punching faults where punching takes place in a position that is offset from the midplane of the empty zone.
Thus, it is not possible for traditional methods to avoid damaging the conductor zone during punching, and that very seriously comprises the quality of the cable.
Furthermore, subsequent operations of connecting the cable to auxiliary electrical members which make use of the orifices that result from the punching as reference points can lead to short circuits, and although they can be avoided by then performing manual adjustment operations, that is laborious and expensive.
An object of the present invention is to resolve the technical problems posed by traditional punching methods by causing the axis of the punch tool to coincide with the midplane of the intermediate empty zone regardless of its dimensions and of its position on the cable.
According to the invention, this object is achieved by means of a method of punching a flat cable having at least one conductor zone defining laterally at least one intermediate empty zone whose midplane is designed to contain the fixed punch axis, wherein:
the cable is caused to pass flat through a lateral guide while using a video system coupled to a computer to monitor the position relative to the punch axis of a reference plane situated in the conductor zone, and it is compared with a reference value corresponding to the ideal position for said reference plane relative to the midplane of the intermediate empty zone so as to measure the offset of said zone relative to the punch axis;
thereafter the cable is displaced transversely and automatically through a distance corresponding to the offset as measured by the computer so as to cause the midplane of the empty zone to coincide with the punch axis; and then
the cable is punched in this position.
In a specific implementation, the reference plane is selected as being the midplane of the conductor zone.
According to an advantageous characteristic, the cable is displaced transversely by controlling a stepper motor acting on the lateral guide of the cable.
In a variant implementation specific to cables having two conductor zones respectively constituted by a group of small-section conductors and by a group of larger-section conductors, the offset of the empty intermediate zone is measured by using the midplane of the group of smaller-section conductors as the reference plane.
According to another characteristic, the video system comprises in particular a camera associated with optical fiber lighting means.
In yet another variant implementation, the position of the reference plane is monitored over a stripped portion of the cable.
Under such circumstances, and preferably, the position of the reference plane is monitored while adjusting the cable longitudinally.
The method of the invention makes it possible to perform punching in complete safety without any risk of damaging the conductors, regardless of the dimensions and the positions thereof across the cable, so long as such positions remain within acceptable tolerances.
The method of the invention makes it possible to use as a reference for determining the optimum position for punching a plane that is immaterial in that it is not mechanically detectable. The punching tool is positioned as a function of the real locations of the conductors and not relative to an edge of the cable.
Punching produces reference orifices for subsequent connections of the cable, which orifices are thus located in positions that are optimal relative to the conductors, and take account of variations in margin and in spacing.
The method is implemented automatically and continuously, thereby making very high rates of throughput possible at a very satisfactory level of quality.